Camshaft support structure

ABSTRACT

Support bases for supporting camshafts in a rotatable manner are mounted on the cylinder head of an internal combustion engine. The support bases are provided so as to be separated from each other in the axial direction of the camshafts. Each of the support bases comprises bearing portions which support the camshafts and a through-hole which extends in the axial direction of the camshafts. A rod is inserted through the through-holes, and the rod restricts the bearing portions from being displaced from positions at which the bearing portions are located while the internal combustion engine is stopped and cold.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national phase application of InternationalApplication No. PCT/JP2011/073339, filed Oct. 11, 2011, the content ofwhich is incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present invention relates to a camshaft support structure thatincludes support bases, which are mounted on the cylinder head of aninternal combustion engine and support camshafts to be freelyrotational.

BACKGROUND OF THE DISCLOSURE

Conventionally, this type of camshaft support structure has beenproposed in, for example, Patent Document 1. According to the camshaftsupport structure disclosed in Patent Document 1, the support bases,which support the camshafts to be freely rotational, are provided apartfrom one another in the axial direction of the camshafts.

With this structure, the weight of the internal combustion engine isreduced as compared to a structure in which an outer frame forconnecting the support bases is provided, as in a ladder-frame camshafthousing, by the weight corresponding to the outer frame.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Laid-Open Patent Publication No. 2010-209796

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

When an engine is operated, the temperature of the cylinder head isincreased by receiving heat of exhaust gas, causing the cylinder head tobe thermally deformed. Since the support bases are arranged to abutagainst the cylinder head, the support bases are thermally deformed byreceiving heat from the cylinder head. This deteriorates alignment ofbearing portions, which are formed in the support bases and support thecamshafts. As a result, problems may arise such as an increase inrotational sliding resistance of the camshafts.

According to the structure disclosed in Patent Document 1, the amount ofheat that the support bases receive from the cylinder head is reduced ascompared to the structure with the ladder-frame camshaft housing by theamount corresponding to the outer frame. The thermal deformation amountof the support bases is thus reduced to some extent. If, however, theinvention is applied to an internal combustion engine in which theexhaust gas temperature is further increased such as an internalcombustion engine provided with a forced-induction device, the amount ofheat that the support bases receive from the cylinder head is furtherincreased. In this case, there are limitations in favorably reducingdeterioration in the alignment of the bearing portions of the supportbases.

Accordingly, it is an objective of the present invention to provide acamshaft support structure that favorably reduces deterioration in thealignment of bearing portions of support bases, which support camshafts,due to engine operation.

Means for Solving the Problems

Means for solving the above issues and advantages thereof will now bediscussed.

To achieve the foregoing objective and in accordance with one aspect ofthe present invention, a camshaft support structure mounted on acylinder head of an internal combustion engine includes support basesfor supporting a camshaft to be freely rotational. The support bases arearranged apart from one another in an axial direction of the camshaft.Each support base has a bearing portion, which supports the camshaft,and a through hole, which extends in the axial direction of thecamshaft. The through holes receive a rod, which restricts the bearingportions from being displaced from an arrangement position at which thebearing portions are located when the internal combustion engine isstopped and cold.

With this structure, the bearing portions of the support bases mountedon the cylinder head of the internal combustion engine support thecamshaft to be freely rotational. Since the support bases are arrangedapart from one another in the axial direction of the camshaft, thecontact area between the support bases and the cylinder head is reducedas compared to the structure with an outer frame for connecting thesupport bases, such as a ladder-frame camshaft housing. This reduces theamount of heat received from the cylinder head, thus reducing thermaldeformation of the support bases caused by the received heat.

Furthermore, with this structure, since the rod is inserted in thethrough holes formed in the support bases, the support bases arerestricted from being thermally deformed by the heat received from thecylinder head.

The rod is assembled to the cylinder head together with the supportbases in a state in which the rod is inserted in the through holes. Thecylinder head is assembled to the cylinder block with head bolts. Thetop surface of the cylinder head is slightly distorted from a flat statedue to the axial tightening force of the head bolts. The rod is thusmaintained in a state pressed by the inner walls of the through holes,and secured to the support bases.

The structure thus favorably reduces deterioration in the alignment ofthe bearing portions of the support bases, which support the camshaft,due to engine operation.

The rod is preferably made of material having higher rigidity than thesupport bases. According to this embodiment, thermal deformation of thesupport bases is reduced in an appropriate manner. In a case in whichthe support bases are made of aluminum alloy, for example, the rod maybe made of stainless-steel, which has higher rigidity than the aluminumalloy.

As a specific structure of the support bases, each support basepreferably includes a receiving member, which is mounted on the cylinderhead and receives the camshaft, and a cap member, which is mounted on atop surface of the receiving member and forms the bearing portiontogether with the receiving member. In this case, the through hole ispreferably formed in the receiving member.

In this case, the support bases preferably receive both an exhaustcamshaft and an intake camshaft, which each serve as the camshaft, andthe through holes are preferably formed closer to the exhaust camshaftthan to the intake camshaft.

In the internal combustion engine, high-temperature exhaust gas isdischarged to an exhaust passage through exhaust valves. The thermaldeformation of the cylinder head is thus greater in the region closer tothe exhaust camshaft. In this point, according to the above embodiment,the through holes in which the rod is inserted are formed closer to theexhaust camshaft than to the intake camshaft. That is, the rod isarranged close to the region of the receiving members of the supportbases where the amount of heat received from the cylinder head is greatand the degree of thermal deformation is great. The region of thesupport bases in the vicinity of the exhaust camshaft where the amountof heat received from the cylinder head is great is thus restricted frombeing thermally deformed in an appropriate manner.

In the internal combustion engine provided with a forced-inductiondevice, since the temperature of exhaust gas is higher than that withoutthe forced-induction device, the thermal deformation amount of thesupport bases caused by heat received from the cylinder head is great.Furthermore, in the internal combustion engine provided with aforced-induction device, since the pressure in the cylinders is higherthan that without the forced-induction device, the cylinder head issignificantly deformed by fluctuation of the pressure in the cylindersof the internal combustion engine. As a result, the deformation amountof the support bases mounted on the cylinder head is increased. Asdescribed above, in the internal combustion engine provided with aforced-induction device, although with the camshaft support structurethat does not include the outer frame for the support bases, thealignment of the bearing portions of the support bases is likely todeteriorate due to engine operation. Applying the present invention tosuch an internal combustion engine favorably reduces deterioration inthe alignment of the bearing portions of the support bases due to engineoperation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating a planar structure of an internalcombustion engine according to a first embodiment of the presentinvention as viewed from above an exhaust camshaft and an intakecamshaft;

FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1,illustrating a cross-sectional structure of the internal combustionengine; and

FIG. 3 is a side view schematically illustrating a side structure of thetop surface of the cylinder head and the support bases mounted on thetop surface in the longitudinal direction of the cylinder head.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A camshaft support structure of a double overhead camshaft (DOHC) inline4-cylinder internal combustion engine according to one embodiment of thepresent invention will now be described with reference to FIGS. 1 to 3.The internal combustion engine of the present embodiment is providedwith an exhaust driven forced-induction device.

FIG. 1 shows a planar structure of an internal combustion engine asviewed from above an exhaust camshaft and an intake camshaft. FIG. 2shows a cross-sectional structure of the internal combustion enginetaken along line A-A of FIG. 1.

A cylinder head 1, which is provided with a valve mechanism includingexhaust valves and intake valves, is provided on the top surface of acylinder block 2 as shown in FIG. 2. The cylinder block 2 and thecylinder head 1 are tightened with head bolts 3 in a known manner (seeFIGS. 2 and 3).

An exhaust camshaft 5 provided with exhaust cams 51 for opening andclosing the exhaust valves and an intake camshaft 6 provided with intakecams 61 for opening and closing the intake valves are arranged on a topsurface 1 a of the cylinder head 1 to be parallel to each other. Morespecifically, five support bases 4 for supporting the camshafts 5, 6 tobe freely rotational are mounted on the top surface 1 a of the cylinderhead 1. Only one of the support bases 4 is shown in FIG. 2.

The support bases 4 are arranged apart from one another in an axialdirection L of the camshafts 5, 6 as shown in FIG. 1. More specifically,the support bases 4 are arranged to be perpendicular to the axialdirection L of the camshafts 5, 6.

Each of the support bases 4 includes a receiving member 41 located onthe top surface 1 a of the cylinder head 1, and an exhaust side capmember 42 and an intake side cap member 43, which are located on the topsurface of the receiving member 41 as shown in FIG. 2. Semi-circularlower recesses 41 b, 41 c are formed on the top surface of eachreceiving member 41 at positions corresponding to the camshafts 5, 6.

A semicircular upper recess 42 b is formed on the bottom surface of eachexhaust side cap member 42 at a position corresponding to the associatedlower recess 41 b. Each lower recess 41 b and the associated upperrecess 42 b form a circular bearing portion 45 b, which supports one ofcam journals 5 a of the exhaust camshaft 5 (see FIG. 1).

Furthermore, a semicircular upper recess 43 c is formed on the bottomsurface of each intake side cap member 43 at a position corresponding tothe associated lower recess 41 c. Each lower recess 41 c and theassociated upper recess 43 c form a circular bearing portion 45 c, whichsupports one of cam journals 6 a of the intake camshaft 6 (see FIG. 1).

Two bolt holes are formed in each exhaust side cap member 42 and theassociated receiving member 41 in an axial direction C of the cylinderswith the exhaust camshaft 5 located in between. The receiving member 41and the exhaust side cap member 42 are tightened to the cylinder head 1with bolts 44L, 44S inserted in the bolt holes.

Furthermore, each intake side cap member 43 and the associated receivingmember 41 are coupled to the cylinder head 1 with other bolts 44L in thesame manner as each exhaust side cap member 42 and the associatedreceiving member 41.

In a state in which the support bases 4 are mounted on the cylinder head1 with the bolts 44L, 44S, the cylinder head 1 is assembled to thecylinder block 2 with the head bolts 3. The cylinder head 1, thecylinder block 2, and the support bases 4 are all made of an aluminumalloy.

In the present embodiment, a through hole 41 d, which extends in theaxial direction L of the camshafts 5, 6, is formed in each receivingmember 41 as shown in FIG. 2. Each through hole 41 d is formed at aposition closer to a center position Pex of the exhaust camshaft 5 thanto a middle position Pc between the center position Pex of the exhaustcamshaft 5 and a center position Pin of the intake camshaft 6 in adirection perpendicular to the axial direction L of the camshafts 5, 6.In other words, the through holes 41 d are formed closer to the exhaustcamshaft 5 than to the intake camshaft 6.

A rod 7 made of stainless-steel is inserted in the through holes 41 d.That is, the rod 7 is made of material having higher rigidity than thesupport bases 4. In the present embodiment, the outer diameter of therod 7 is slightly smaller than the inner diameter of the through holes41 d. The bolts 44S located closer to the rod 7 than to the exhaustcamshaft 5 are shorter than the other bolts 44L so as not to interferewith the rod 7.

Operation of the present embodiment will now be described.

The camshafts 5, 6 are supported to be freely rotational by the bearingportions 45 b, 45 c of the five support bases 4 mounted on the cylinderhead 1. Since the support bases 4 are located separate from one anotherin the axial direction L of the camshafts 5, 6, the contact area betweenthe support bases 4 and the cylinder head 1 is reduced as compared to acase in which an outer frame for connecting the support bases isprovided, as in a ladder-frame camshaft housing. The amount of heatreceived from the cylinder head 1 is thus reduced, which reduces thermaldeformation of the support bases 4 caused by receiving heat.

Since forced induction is performed by the forced-induction device inthe internal combustion engine of the present embodiment, thetemperature of exhaust gas is increased as compared to the internalcombustion engine without a forced-induction device. This increases thethermal deformation amount of the support bases 4 caused by receivingheat from the cylinder head 1. Furthermore, since the pressure in thecylinders is also increased as compared to the internal combustionengine without the forced-induction device, the cylinder head 1 isdeformed significantly as the pressure in the cylinders of the internalcombustion engine fluctuates. The deformation amount of the supportbases 4 mounted on the cylinder head 1 is consequently increased. Asdescribed above, in the internal combustion engine provided with theforced-induction device, the alignment of the bearing portions 45 b, 45c in the support bases 4 is likely to deteriorate due to engineoperation although with the camshaft support structure of the presentembodiment that does not include the outer frame for the support bases4.

In this respect, since the rod 7 is inserted in the through holes 41 dformed in the support bases 4 in the present embodiment, the supportbases 4 are favorably restricted from being thermally deformed due toheat received from the cylinder head 1.

Furthermore, in the internal combustion engine, high-temperature exhaustgas is discharged to the exhaust passage through the exhaust valves.Thermal deformation of the cylinder head 1 is thus increased toward theregion close to the exhaust camshaft 5. In this respect, with theabove-mentioned structure, the through holes 41 d in which the rod 7 isinserted are formed at positions closer to the exhaust camshaft 5 thanto the intake camshaft 6. That is, the rod 7 is arranged in the vicinityof the regions in the receiving members 41 of the support bases 4 wherethe amount of heat received from the cylinder head 1 is great and thedegree of thermal deformation is great. Thermal deformation of thereceiving members 41 in the vicinity of the exhaust camshaft 5 is thusreduced in an appropriate manner.

Furthermore, the rod 7 is assembled to the cylinder head 1 together withthe support bases 4 in a state in which the rod 7 is inserted in thethrough holes 41 d. The cylinder head 1 is further assembled to thecylinder block 2 with the head bolts 3 in a state in which the supportbases 4 and the rod 7 are assembled to the cylinder head 1. In thisembodiment, the top surface 1 a of the cylinder head 1 is slightlydistorted from a flat state due to the axial tightening force of thehead bolts 3 as shown in FIG. 3. The rod 7 is thus maintained in a statepressed by the inner walls of the through holes 41 d, and secured to thesupport bases 4. For the illustrative purposes, the distortion of thetop surface 1 a of the cylinder head 1 is exaggerated and the rod 7 isomitted in FIG. 3.

The camshaft support structure of the present embodiment as describedabove has the following advantages.

(1) The support bases 4 are arranged apart from one another in the axialdirection L of the camshafts 5, 6. Furthermore, the bearing portions 45b, 45 c, which support the camshafts 5, 6, and the through holes 41 d,which extend in the axial direction L of the camshafts 5, 6, are formedin the support bases 4. The rod 7 is inserted in the through holes 41 dto restrict the bearing portions 45 b, 45 c from being displaced fromthe arrangement position at which the bearing portions 45 b, 45 c arelocated when the internal combustion engine is stopped and cold. Withthis structure, in the support bases 4, which support the camshafts 5,6, the alignment of the bearing portions 45 b, 45 c is favorablyrestricted from deteriorating due to engine operation. The state inwhich the internal combustion engine is stopped and cold refers to astate in which operation of the internal combustion engine is stoppedand the influence of heat caused by the previous engine operation can beignored.

(2) The rod 7 is made of material having higher rigidity than thesupport bases 4. More specifically, the support bases 4 are made of analuminum alloy, and the rod 7 is made of stainless-steel, which hashigher rigidity than the aluminum alloy. With this configuration,thermal deformation of the support bases 4 is reduced in an appropriatemanner.

(3) The through holes 41 d are formed closer to the exhaust camshaft 5than to the intake camshaft 6. This structure appropriately reducesthermal deformation of the receiving members 41 in the vicinity of theexhaust camshaft 5 where the amount of heat received from the cylinderhead 1 is great.

The camshaft support structure of the present invention is not limitedto the structure illustrated in the above described embodiment, but maybe modified as follows.

In the above-described embodiment, the present invention is applied toan internal combustion engine provided with an exhaust drivenforced-induction device, that is, a turbocharger. The present inventionmay, however, be applied to an internal combustion engine provided withan engine driven forced-induction device, or a supercharger.

In the above-described embodiment and the modified embodiment, thepresent invention is applied to an internal combustion engine providedwith a forced-induction device. The present invention, however, is notonly applied to an internal combustion engine provided with aforced-induction device, but may be applied to an internal combustionengine without a forced-induction device. In this case, although theamount of heat the support bases receive from the cylinder head is smallas compared to that received by the engine provided with theforced-induction device, the alignment of the bearing portions of thesupport bases is favorably restricted from deteriorating due to engineoperation in the same manner as the above-described embodiment.

As in the above-described embodiment, it is preferable that the throughholes 41 d be formed closer to the exhaust camshaft 5 than to the intakecamshaft 6 to prevent thermal deformation of the receiving members 41 inthe vicinity of the exhaust camshaft 5 where the amount of heat receivedfrom the cylinder head 1 is great. The present invention, however, isnot limited to this, but through holes may be formed at, for example,the middle position Pc between the exhaust camshaft 5 and the intakecamshaft 6. In this case also, thermal deformation of the receivingmembers is restricted to some extent.

In the above-described embodiment, one through hole 41 d is formed ineach of the support bases 4. Instead, two or more through holes may beformed in each of the support bases 4, and two or more rods may beprovided corresponding to the number of the through holes. This furtherreduces thermal deformation of the support bases.

The rod 7 made of stainless-steel is illustrated in the above-describedembodiment, but the rod may be made of any material that has higherrigidity than the support bases.

DESCRIPTION OF THE REFERENCE NUMERALS

1 . . . cylinder head, 1 a . . . top surface, 2 . . . cylinder block, 3. . . head bolt, 4 . . . support base, 41 . . . receiving member, 41 a .. . abutment surface, 41 b, 41 c . . . lower recesses, 41 d . . .through hole, 42 . . . exhaust side cap member, 42 b . . . upper recess,43 . . . intake side cap member, 43 c . . . lower recess, 44 . . . bolt,45 b, 45 c . . . bearing portions, 5 . . . exhaust camshaft, 5 a . . .cam journal, 51 . . . exhaust cam, 6 . . . intake camshaft, 6 a . . .cam journal, 61 . . . intake cam, 7 . . . rod.

1.-5. (canceled)
 6. A camshaft support structure mounted on a cylinder head of an internal combustion engine, the camshaft support structure comprising support bases for supporting both an exhaust camshaft and an intake camshaft to be freely rotational, the structure comprising: the support bases are arranged apart from one another in an axial direction of the exhaust camshaft and the intake camshaft; each support base has bearing portions, which support the exhaust camshaft and the intake camshaft, and a through hole, which is formed closer to the exhaust camshaft than to the intake camshaft and extends in the axial direction; and the through holes receive a rod, which restricts the bearing portions from being displaced from an arrangement position at which the bearing portions are located when the internal combustion engine is stopped and cold.
 7. The camshaft support structure according to claim 6, wherein the rod is made of material having higher rigidity than the support bases.
 8. The camshaft support structure according to claim 6, wherein each support base includes a receiving member, which is mounted on the cylinder head and receives the exhaust camshaft and the intake camshaft, and cap members, which are mounted on a top surface of the receiving member and form the bearing portions together with the receiving member, and the through hole is formed in the receiving member.
 9. The camshaft support structure according to claim 6, wherein the internal combustion engine includes a forced-induction device. 